The present invention relates to computer apparatus and, more particularly, to a redundant storage selection means for such a computer apparatus.
In a computer system, there are a number of different types of memory or storage units employed to store the various forms of information required in the operation of the computer. There are registers, latches, and flip-flop circuits at one end of the scale. These are used for the temporary storage of small units of data during the operation of the computer. There are also core storage units and transister logic storage units for random access memories in the middle range of the scale. These are relatively small in storage capacity although larger than the registers and latches. These random access memories are also usually used for the storage of work in progress albeit for somewhat larger blocks of data. These storage units have the advantage of extremely rapid access to the stored data or for the storage for data therein. They do not have the storage capacity needed for the bulk storage of the great mass of data handled by a computer. For such bulk storage, units such as magnetic drum memories or magnetic disc file memories are used. While these bulk storage units do have the storage capacity to store large volumes of data, because they involve rotating mechanisms, their access time is substantially slower than that of the units previously mentioned. Because these magnetic units do not exhibit a high order of reliability, it has been found desirable to store the same information in more than one place in such memory units. The redundant storage of data enhances the reliability of the storage system. If advantage is taken of the separate locations of the redundant storage, rather than merely relying on the additional storage in the event of failure of primary storage location, the average access time to the stored data can be substantially reduced.